A number of 5-alkyl resorcinols are known. Such compounds have a variety of utilities, including that of being important starting materials in the synthesis of 1-hydroxy-3-alkyl-dibenzopyran derivatives. Adams et al. discovered that the biological activity of such dibenzopyran derivatives could be increased by introducing branching at the 1'-position of the 3-alkyl moiety, see J. Am. Chem. Soc. Vol. 70, 664 (1948). It accordingly became necessary to prepare 5-(tertiary alkyl)resorcinols which could be used in the preparation of such dibenzopyrans having highly branched side-chains in the 3-position. The synthesis of 5-(tertiary alkyl)resorcinols was particularly difficult, as demonstrated by the process disclosed by Adams et al., ibid. Such process included the conversion of 3,5-dimethoxybenzoic acid to 3,5-dimethoxybenzaldehyde, which upon reduction afforded 3,5-dimethoxybenzyl alcohol. Chlorination afforded 3,5-dimethoxybenzyl chloride, which was then converted to 3,5-dimethoxybenzyl cyanide. Dialkylation of this latter compound provided 3,5-dimethoxy-.alpha.,.alpha.-dimethylbenzyl cyanide, which when reacted with n-pentyl magnesium bromide afforded 3,5-dimethoxy-(1,1-dimethyl-2-oxoheptyl)-benzene. Reduction of this latter named compound provided the corresponding alcohol which was next dehydrated to the corresponding alkene, and finally reduction of such alkene afforded 3,5-dimethoxy-(1,1-dimethylheptyl)benzene. Demethylation of the latter compound afforded the desired resorcinol.
It is clear from the foregoing that such processes for preparing resorcinol intermediates are unattractive from a commercial standpoint due to the length of the overall process and cost of starting materials. Very little developmental work has been attempted with Adam's process in an effort to simplify that process or to devise a better process for preparing 5-(tertiary alkyl)resorcinols. An object of this invention is to provide a simple and efficient process for preparing 5-(tertiary alkyl)resorcinols. It has now been discovered that 2,6-dimethoxyphenol surprisingly is alkylated almost exclusively at the 4-position by reaction with a tertiary carbinol in the presence of an acid. Such alkylation provides a 1-hydroxy-2,6-dimethoxy-4-(tertiary alkyl)benzene which can readily be converted to a 5-(tertiary alkyl)resorcinol. Such process affords high yields of the desired 5-(tertiary alkyl)resorcinol in only four steps, and starting from relatively inexpensive starting materials.